1. Field of the Invention
This invention relates to an abnormal combustion detecting construction for a burner adapted to burn fuel such as gaseous fuel, liquid fuel and the like using air and more particularly to such an abnormal combustion detecting construction which is adapted to rapidly and effectively detect abnormal combustion in a burner, particularly that causing an excessively or abnormally increased flame.
2. Description of the Prior Art
Conventionally, it has been highly desired to detect abnormal combustion of a burner utilizing a variation of an oxygen concentration in the burner.
For this purpose, there have been proposed several mechanisms or devices for detecting a variation of an oxygen concentration in a burner to monitor combustion state of the burner. One of the conventional detecting devices is disclosed in Japanese patent application Laid-Open Publication No. 93116/1984 (Japanese patent application No. 201502/1982). The detecting device disclosed includes a temperature detecting element such as a thermocouple which serves to sense a combustion temperature in a burner to detect a deterioration of combustion due to lack of oxygen. However, the detecting device, as described above, is adapted to secondarily or indirectly detect a variation of an oxygen concentration in a burner, so that it fails to effectively and positively detect the variation with good reliability.
Another conventional device for detecting a variation of an oxygen concentration in a burner is disclosed in Japanese patent application Laid-Open Publication No. 80758/1985 (Japanese patent application No. 190440/1983). The device disclosed is so constructed that a flame current detecting electrode is arranged in a manner to project into a flame formed due to combustion in a burner to detect a variation of a flame current flowing therethrough during the combustion, to thereby sense a decrease in an oxygen concentration in air supplied to the burner. Unfortunately, the device likewise fails to reliably detect a variation of the oxygen concentration because it is indirectly detected.
Japanese Patent Publication No. 5518/1968 discloses a conventional detecting device of another type which is constructed to detect the extinguishing of a combustion flame in a burner due to a difference between an oxygen concentration in the combustion flame and that in an ambient atmosphere which is detected by means of platinum electrodes attached to an electrically conductive ceramic substrate. However, such construction fails to not only detect in advance abnormal combustion in a burner which leads to the extinguishing of a combustion flame but sense abnormal combustion causing an excessively or abnormally increased flame. Also, it highly complicates a structure of the burner.
An additional conventional detecting device is disclosed in Japanese Patent Publication No. 28892/1986, which is constructed in a manner to position an oxygen deficiency detecting sensor in a catalyst casing arranged at an upper section of a combustion chamber to cause exhaust gas produced in the combustion chamber to be constantly passed through the sensor, to thereby monitor an oxygen concentration in the exhaust gas. However, the detecting device is not adapted to effectively and positively detect oxygen deficiency unless an oxygen concentration and a carbon monoxide concentration in the combustion chamber are highly decreased and increased, respectively, because the whole oxygen deficiency detecting sensor is arranged in the combustion chamber.
Accordingly, it would be highly desirous to develop an abnormal combustion detecting construction which is capable of directly detecting a variation of an oxygen concentration in a combustion chamber of a burner with good reliability to effectively monitor abnormal combustion in the burner.